The primary component of lithographic printing inks is a gelatinous or gelled vehicle or carrier that must possess sufficient viscosity to disperse finely divided pigments, anti-abrasion additives, and other solid components. Historically, the vehicle or carrier has been based on hydrocarbon based resins, and the control of the rheology of the ink vehicle has historically been challenging. In order to achieve the required gel structure, gelants must be added to the resin. Typical gelants are the aluminum acylates or alkoxides as described in U.S. Pat. No. 5,427,615 and modified clays as described in U.S. Pat. No. 4,193,806. Other molecular gelants such as polyamide resins and styrene-butadiene block copolymers have been used as gelants in hydrocarbon based oils and solvents. There are several undesirable aspects associated with the use of these gelants.
Organoaluminum based gelants are typically provided in solvents at low concentration of the active aluminum component thus increasing the percentage of VOC's in the formulation. Heat is required for gelation to occur and precise temperature control is required or the gel structure can be destroyed. The modified clays also require heat and sometimes high shear is required to activate or open the clay structure in order for gelation to occur. Polyamide and block copolymer based gelants must be used at high weight percent loadings, typically 20 percent or higher, in order to achieved the desired viscosity. In addition all of these gelants add substantially to the cost of the ink vehicle.
There has been considerable interest in developing vehicles or carriers for oil-based printing inks that do not require petroleum or hydrocarbon based components. Decreasing supplies of petroleum, environmental concerns, and interest in biodegradable and renewable resources have prompted the ink manufacturers to initiate efforts to develop inks with vehicles based on biodegradable materials to reduce the industry's dependency on petroleum. 1) (“Vegetable-Oil-Based Printing Ink Formulation and Degradation”. Erhan, S. Z, Bagby, M. O. Industrial Crops and Products. 3 (1995). 237-246. 2) “Vegetable Oil-Based Printing Inks”. Erhan, S. Z, Bagby, M. O. JAOCS, Vol. 69, no. 3 (1992) 251.
The primary means for increasing the viscosity or gelation of natural oils has historically been referred to as “heat-bodying” the oil. In this process, unsaturated natural oils are subjected to high temperatures, typically 300-340 deg C. in an inert atmosphere in order to promote chemical crosslinking at the sites of unsaturation in the triglyceride oil. This process as described in U.S. Pat. Nos. 5,122,188 and 6,418,852 typically results in oils with viscosities in the range 1600-1800 centipoise. In order to obtain higher viscosities, a second type of heat-bodying process is employed in which the high temperature heating is continued until the oil is irreversibly gelled. This intractable gel is then heated at about 340 deg C. with unmodified oil to produce the desired viscosity. It is often necessary to filter insoluble clumps of gelled oil from these blends. In addition, because both of these processes result in irreversible chemical crosslinks between the triglyceride oil chains; it is difficult to maintain obtain precise control of the viscosity. Both of these processes also require rigorous exclusion of oxygen in order to prevent oil degradation and discoloration.
The present invention discloses gelled natural oils useful as ink vehicles and a novel method for their production. The natural oil gelled ink vehicles of the present invention offer several advantages over gelled vehicles disclosed in prior art in that no gelants are required and “heat-bodying” of the oil is unnecessary. The viscosities of the natural oil gelled ink vehicles may also be precisely controlled.